1. Field of the Invention
The present invention relates to a motor control device for a powered seat used in a vehicle having a seating posture adjusting system therein to effect an adjustment in positions of the seat to support an occupant at a desired level, such as for adjusting fore-and-aft and vertical positions or support inclination angle of the seat, headrest or side support device.
2. Description of Prior Art
By and large, a vehicle or automotive seat is equipped with such seating posture adjusting system as a seat slide device, seat lifter, reclining device, movable headrest, side support device, and the like. In particular, a driver's seat is equipped with a lot of these adjusting systems with a view to giving a most seating preference or comfort to a driver on the seat, according to his or her physical constitution, the road conditions, and fatigue developed during a lengthy time of driving the car.
The adjustments of this sort are now executed under an electronic motor control on a switch operation basis, instead of a manual one, to deal with frequent adjustments with rapidity and ease during driving. Such demand produces what is recentlY called "powered seats" which has electrical and electronic control systems provided therein for enabling various multiple adjustments of the seat by simple operation of switches.
The motions or adjustments in such powered seat are actuated by a motor, and the control of the motor is a key to present variety of motions in the seat for many desired adjustments thereof. For instance, the normal or reverse rotation of the motor is effected by turning the switch to a corresponding "on" state, using a self return type switch having three switch positions: a neutral position, normal position and reverse position. The electrical communication between the switch and motor is supported by a relay and associated relay control circuits. Hence, an instruction signal from the switch activates the relays to switch-over the relay contact points in order to apply a given amount of voltage to the motor for causing motor to rotate in either a normal or reverse directions.
This on-off switch system provides only a given amount of voltage to the motor, and therefore the motor gives a fixed force to cause non-variable speed in adjustments of the powered seat. Hitherto known motor control systems have encountered such technical bar in contemplating fine and quick adjustments of the drive rate (speed) of the motor.
A possible solution to this problem may be for forming two motor control circuits: a high motor rate control and a low motor rate control connecting them electrically with the motor by two separate self return type switches. However, such circuit formation results in a very complicated construction of the control system and an annoying operation of the switches.